What’s cooler than cool?

For the astronomer who helped identify ocean water on one of Jupiter’s moons, it was pretty cool that scientists were able to determine magnesium sulfate salt, or epsomite, was the substance bubbling up to Europa’s surface.

But what was even cooler, Astronomer Mike Brown said, is how he and other scientists made the discovery.

“From setting up on top of Mauna Kea, we could do things you couldn’t do with a spacecraft flying by” the moon of Jupiter, said Brown, a professor of planetary astronomy at the California Institute of Technology. The observatories may age, but “you keep on putting new equipment on the telescope.”

Brown and Kevin Hand, from the NASA Jet Propulsion Laboratory, used W.M. Keck Observatory a little more than a year ago to get the images of Europa, which they then studied at the Jet Propulsion Laboratory. Even 400 million miles away from Europa, Keck’s images, using Adaptive Optics and OH-Suppressing Infrared Integral Field Spectrograph, were much clearer than the Galileo mission’s from a little more than a decade ago.

Work on the spacecraft used in NASA’s Galileo mission first started in 1977, and the craft launched in 1989, with the mission ending in 2003. Brown said the technology used then sent back fuzzy images of the spectra — basically the infrared light fingerprint of material on Europa’s surface. The images showed there was more than just water on the moon, but were not clear enough to identify the materials, although magnesium sulfate was one material scientists suspected was there.

Magnesium sulfate shouldn’t be on the planet’s surface, and the magnesium sulfate had to somehow come through that thick, icy shell, to be detected, Brown said. If salt from the ocean is on the planet’s surface, that also means surface material could be down in the ocean, he added.

Europa has more water than Earth. With water, scientists say, comes the increasing possibility of finding life.

“It’s a very cool place to wonder about,” Brown said.

If someone could land on Europa right now, they could scoop up material from the surface and get access to information about what’s in the ocean, without having to drill through that thick, icy crust, Brown added. The technology is available to do so, he said, although no one has the funds to launch such a mission.

Scientists believe the magnesium sulfate may come from another of Jupiter’s moons, Io, in the form of volcanic emissions, which eventually reach Europa, Keck officials said.

Brown and Hand first plotted the distribution of pure water ice versus anything else on Europa’s surface. Then, looking at low altitudes in a particular area, they found a “tiny dip” in the spectrum scientists hadn’t seen before, Keck officials said. Brown said no one previously noticed the dip because they weren’t able to zoom in close enough to see it.

Brown said they compared the spectrum with spectra they obtained in their labs, including that of Drano. The pipe-clearing chemical is sodium hydroxide, which consists of elements that could have been the material, Brown said.

“We tried to think outside the box to consider all sorts of other possibilities, but at the end of the day, the magnesium sulfate persisted,” Hand said in a news release about the discovery.

Brown said they got the images from Keck about 14 months ago, and by last summer, they were certain the material was the magnesium sulfate. Their paper on the discovery was published in The Astronomical Journal.